More Highways, Less Pollution

New report ignores positive trends

Environmental activists continue to mis-diagnose air pollution’s causes and cures and to obscure or ignore positive trends in pollution emissions and ambient levels. “Highway Health Hazards,” a new report from the Sierra Club, is the latest example.

Of course, all else equal, more driving means more pollution. But the U.S. has achieved large pollution reductions in spite of rapid growth in driving. For example, between 1975 and 2003 total vehicle miles driven increased by more than 110%, but the average number of 8-hour ozone exceedances per year decreased more than 60%, and the average number of 1-hour ozone exceedances per year decreased more than 90%. Average levels of fine airborne particulate matter (PM2.5) decreased more than 40%. Where 60% of the nation’s monitoring locations violated the 1-hour ozone standard in the late 1970s, only 10% do so today. All other pollutants declined as well and virtually the entire nation attains federal air standards for carbon monoxide, nitrogen dioxide, and lead.

Technology is winning the war on air pollution by decreasing emissions per vehicle much more rapidly than driving is increasing. Fleet turnover to inherently cleaner vehicles ensures these improvements will continue.

You won’t see any of this good news in “Highway Health Hazards.” The Sierra Club instead makes the ridiculous claim that “the number of regions with unhealthy air will more than double in the next few years.” And despite the fact that automobile emissions per mile are dropping by about 10% per year, while miles driven is increasing only about 2% per year, a heading in the report proclaims “More Highways, More Sprawl, More Pollution.” Indeed, the report discusses increases in driving, but provides no data at all on actual trends in vehicle emissions or ambient pollution levels.

While the Sierra Club misleads the public about driving and air pollution, most of “Highway Health Hazards” is devoted to highlighting scary conclusions from cherry-picked air pollution health studies. For example, the report summarizes the American Cancer Society (ACS) study of particulate matter and mortality, which reported an association between higher PM2.5 and risk of death, but omits a study of veterans that found no such link, even though the veterans all had high blood pressure and should therefore have been more susceptible to any PM effects.1 Also ignored is that fact that even the ACS study found no PM-mortality association for women, those with more than a high school degree, former smokers, and the moderately active — a biologically implausible collection of results that calls the validity of the entire study into question.

The Sierra Club was also selective about what information it provided from each study it did choose. For example, the Club cites a Denver study that reported that living near busy roads was associated with higher rates of childhood leukemia, but fails to mention that the study was based on cancer incidence data collected from 1976 to 1983 and traffic data from 1990.

Compared to today, the average diesel truck emitted about six times as much soot per mile during the mid-1970s, while the average car emitted about 10 times as much volatile organic compounds (VOC). The Denver study reported that elevated cancer incidence was associated only with living near roads that carry more than 20,000 vehicles per day. So to get an equivalent amount of pollution today, you’d have to live near a road that carries at least six times as much traffic.

The Sierra Club also omits the original study’s qualifications of its results. The study was not based on pollution levels, but only on traffic counts. As with all epidemiologic studies, this one is subject to statistical confounding and bias, which could create the appearance of a cause-effect relationship where none actually exists. The study authors noted “Noise, increased light exposure, or some socioeconomic factor may also help explain these results.” The study was also based on relatively small samples — only eight children with leukemia and three controls lived near roads that carried more than 20,000 vehicles per day.

An ironic feature of the Sierra Club’s ostensible concern for people’s health is that implementing the Club’s recommendations would actually increase people’s exposure to vehicle pollution. Compared to dense cities, suburbs spread driving out over a wider land area. All else equal, this means lower ambient pollution concentrations for a given total amount of driving. Of course, per-capita driving is lower in denser areas, but not by nearly enough to make up for the increase in density. Thus, despite having greater transit use, denser cities also have more traffic congestion and more concentrated vehicle emissions, as anyone who has walked the streets of Manhattan can attest.

The Sierra Club ignores the inconvenient fact that suburbs and automobile-based lifestyles are not foisted upon the public, but are voluntarily chosen. A recent study by researchers from Harvard and Tufts concluded that suburbanization has indeed improved people’s overall welfare, and that as people get wealthier they are more likely to choose suburbs and to drive more. Perhaps people know more about their preferences than the Sierra Club’s “experts.”

The Sierra Club also doesn’t seem to know much about the best ways to reduce air pollution, despite its willingness to propose sweeping and costly reorganizations of Americans’ lives in the name of air pollution reduction. A wide range of pollution studies have shown that a small fraction of all cars produces most automobile pollution. For example, based on recent on-road remote sensing measurements the worst 5% of cars produce 50% of automobile VOC emissions, and the worst 10% produce 70%. Thus, policies that aim to decrease overall driving miss the target, since, even if effective, most of the effort and expense would go into reducing miles driven by the vast majority of cars that produce only a few percent of all vehicle pollution.

Land-use and transit are also ineffective as air pollution control measures. Metropolitan areas that plan to increase urban density and spend billions on transit over the next 20 years predict that all this effort will reduce future driving by at most a few percent below “business as usual.” Meanwhile, we could reduce total automobile VOC emissions by as much as 40% right now and at a fraction of the cost of transit and growth management, simply by identifying and repairing or scrapping the worst few percent of the vehicle fleet. Furthermore, since the average vehicle on the road will be about 90% cleaner in 15 or 20 years, any long-term efforts to reduce driving will be irrelevant to air pollution by the time they come to fruition.

It’s no surprise that the Sierra Club fails to discuss positive air pollution trends and the problems with its policy prescriptions, and ignores people’s lifestyle preferences. After all, the Sierra Club’s goal is to override people’s individual choices and instead bend them to its collectivist vision of how people ought to live — all for their own good, of course. As Adam Smith aptly put it more than 200 years ago “virtue is more to be feared than vice, because its excesses are not subject to the regulation of conscience.”

Joel Schwartz is an adjunct fellow at Reason Foundation and visiting scholar at American Enterprise Institute.


1. A more detailed discussion of PM and mortality can be found here: